Superconducting wires or tapes have been developed based upon high temperature superconducting (HTc) materials which may have critical temperatures TC above 77 K, facilitating their use in cryogenic systems cooled by liquid nitrogen. In certain applications, such as use in superconducting fault current limiters (SCFCL), high temperature superconducting (HTS) tapes may experience high temperature excursions in the case of a fault, in which the superconducting layer undergoes a transition to non-superconducting state.
When a fault occurs in an SCFCL, due to the finite resistance acquired by the superconducting layer, current that is conducted almost exclusively through the superconductor layer under normal operation of the SCFCL is diverted into metallic layers that are in contact with the superconductor layer, which layers typically present lower resistance than the now-resistive superconductor layer. The current passing through the metallic layers during the fault condition may cause resistive heating that generates temperatures up to 400 C. or more in the HTS tape. As a result of high temperatures, roughening of metal surfaces as well as oxidation may take place in local spots or at a metal layer interface, leading to degradation of the metallic layers and reducing the lifetime of the HTS tape.
On the other hand, in order to effect a significant voltage drop along the length of the superconductor tape, it may be desirable to increase the sheet resistance of the metallic layers in the HTS tape. Although this could in principle be accomplished by decreasing the thickness of a metal layer such as copper, the reduced thickness may lead to increased susceptibility to agglomeration or other degredation that may shorten the HTS tape lifetime. It is with respect to these and other considerations that the present improvements are needed.